Parkinson Disease:
A progressive, degenerative neurologic disease characterized by a Tremor that is maximal at rest, retropulsion (i.e. a tendency to fall backwards), rigidity, stooped posture, slowness of voluntary movements, and a masklike facial expression. Pathologic features include loss of melanin containing neurons in the substantia nigra and other pigmented nuclei of the brainstem. Lewy bodies are present in the substantia nigra and locus coeruleus but may also be found in a related condition (Lewy body disease, Diffuse) characterized by dementia in combination with varying degrees of parkinsonism. (Adams et al., Principles of Neurology, 6th ed, p1059, pp1067-75)

1Center for Visual and Neurocognitive Rehabilitation, Atlanta VAMC, Department of Medicine, Division of General Medicine and Geriatrics, Emory University School of Medicine, 2Harvard Neurology Residency Program, Brigham and Woman‘s Hospital and Massachusetts General Hospital

1Department of Otolaryngology - Head and Neck Surgery, University of Missouri, 2Department of Communication Science and Disorders, University of Missouri, 3Department of Medicine, University of Missouri

1Center for Metabolic and Degenerative Diseases, The Brown Foundation Institute of Molecular Medicine, Programs in Human and Molecular Genetics and Neuroscience, The Graduate School of Biomedical Sciences at Houston, The University of Texas Health Science Center at Houston, 2Department of Natural Sciences, University of Houston - Downtown, 3Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center at Houston

1Program in Physical Therapy, Washington University School of Medicine, 2Program in Occupational Therapy, Washington University School of Medicine, 3Department of Neurology, Washington University School of Medicine, 4Mallinckrodt Institute of Radiology, Washington University School of Medicine, 5Department of Biomedical Engineering, Washington University